Stents are generally cylindrical-shaped devices that are radially expandable to hold open a segment of a vessel or other anatomical lumen after implantation into the body lumen.
Various types of stents are in use, including expandable and self-expanding stents. Expandable stents generally are conveyed to the area to be treated on balloon catheters or other expandable devices. For insertion into the body, the stent is positioned in a compressed configuration on the delivery device. For example, the stent may be crimped onto a balloon that is folded or otherwise wrapped about the distal portion of a catheter body that is part of the delivery device. After the stent is positioned across the lesion, the balloon is expanded by the delivery device, causing the diameter of the stent to expand. For a self-expanding stent, a sheath covering the stent is retracted allowing the unconstrained stent to expand, the physiological conditions at the placement site cause the stent to expand, or the combination causes the stent to expand.
Stents are used in conjunction with balloon catheters in a variety of medical therapeutic applications, including intravascular angioplasty to treat a lesion such as plaque or thrombus. For example, a balloon catheter device is inflated during percutaneous transluminal coronary angioplasty (PTCA) to dilate a stenotic blood vessel. When inflated, the pressurized balloon exerts a compressive force on the lesion, thereby increasing the inner diameter of the affected vessel. The increased interior vessel diameter facilitates improved blood flow. Soon after the procedure, however, a significant proportion of treated vessels restenose.
To reduce restenosis, stents constructed of metals or polymers are implanted within the vessel to maintain lumen size. The stent is sufficiently longitudinally flexible so that it can be transported through the cardiovascular system. In addition, the stent requires sufficient radial strength to enable it to act as a scaffold and support the lumen wall in a circular, open configuration. Configurations of stents include a helical coil, and a cylindrical sleeve defined by a mesh, which may be supported by a stent framework of struts or a series of rings fastened together by linear connecter portions.
Unfortunately, stent insertion can cause undesirable reactions such as inflammation resulting from a foreign body reaction, infection, thrombosis, and proliferation of cell growth that occludes the blood vessel. Polymer coatings applied to the surface of stents have been used to deliver drugs and other therapeutic agents at the placement site of the stent in order to reduce the incidence of deleterious conditions including thrombosis and restenosis.
It would be desirable to provide a biodegradable medical device with hydroxyapatite filaments and/or biodegradable polymer fibers that overcomes the disadvantages described above.